F.Fressin, T.Guillot

1. A STEP Antarctica Search for Transiting Extrasolar Planets F.Fressin, T.Guillot Y.Rabbia, A.Blazit, JP. Rivet, J.Gay, D.Albanese, V.Morello, N.Crouzer (OCA - Nice), F.X Schmider, K.Agabi, J-B. Daban, E.Fossat, L.Abe, C.Combier,F.Janneaux,Y. Fantei (LUAN – Nice) C.Moutou, F.Bouchy, M.Deleuil, M.Ferrari, A.Llebaria, M.Boer, H.Le Corroler, A.Klotz,A.Le van Suu,J. Eysseric, C Carol (OAMP - Marseille), A.Erikson, H.Rauer (DLR - Berlin), F.Pont (Obs. Genève)

2. Transit spectroscopy offers additional possibilities not accessible for “normal” planets The future of transit searches Combined to radial-velocimetry, it is the only way to determine the density, hence the global composition of a planet We foresee that exoplanetology will have as its core the study of transiting exoplanets examples: A correlation between the metallicity of stars and planets (Guillot et al. A&A 2006) Planetary formation model constraints (Sato et al 2005)

3. The future of transit searches • 2 future milestones: • COROT: 60 000 stars (nominal mission), mv=11 to 16, for 150 days, launch oct. 2006 • KEPLER: 100 000 stars, mv=11 to 14 for 4 years, + 70 000 for 1 year, launch end 2008 • Limited by data transmission to Earth • A problem for the detection of small planets: background eclipsing binaries • Future missions should: • Detect more planets • Diversify the targets • Detect smaller planets • from SPACE • Natural but costly • Limited in telescope size, number of instruments... • from DOME C • Promising but uncertain • Requires precursor mission(s)

4. Why transit searches at Dome C? • Continuous night for 3 months • Excellent weather • Questions: • We don’t know how the following factors will affect transit surveys: • Sky brightness & fluctuations • Presence of the moon • Generally, systematics effect due to the combination of astrophysical, atmospheric and instrumental noises • Technical problems • Autonomous operations in cold (-50°C to -80°C) conditions • Temperature fluctuations • Icing • Electrical discharges

5. A STEP Objectives Determine the limits of Dome C for precise wide field photometry (Scintillation and photon noise … or other noise sources ?) If the site is competitive with space and transit search limits are well understood, establish the bases of a mid-term massive detection project (large Schmidt telescope or network of small ones) Search for transiting exo-planets and characterization of these planets – Detection of bright stars oscillations.

6. A STEP: the philosophy behind • Prepare future photometric projects for planetary transit detection at Dome C • Use available equipment, minimize development work for a fast implementation of the project • Use experience acquired from the site testing experiment Concordiastro • Semi-automated operation • Directly compare survey efficiency at Dome C with BEST 2 in Chile for the same target field

7. Ground based transit projects 10 transiting planets discovered up to date • 4 radial velocities + photometric follow up • 5 OGLE • 1 STARE/TrES

8. Transits photometry – Any problem ? A huge difference between the expected number of detections and reality : Project STARE OGLE HATnet Vulcan UNSW Number of detections expected per season 14 17.2 11 11 13.6 Real number of detections 1 1.2 0 0 0 Simulation considering « systematic effects » 0.9 1.1 0.2 0.6 0.01 DUTY CYCLE These numbers really depend of the duty cycle of each campaign Red Noise These red noises, or «systematic effects » are all the noises undergoing temporal correlations and that we can not subtract easily.

9. Systematic effects (F.Pont 2005) • We only have a partial knowledge of these effects • They seem to all result from interaction between environmental effects with instrumental characteristics (Pont 2005) • They are closely linked to the spatial sampling quality • For OGLE, the principal source is differential refraction linked to air mass changes. (Zucker 2005) —magnitude dependence with white noise —magnitude dependence with red noise

10. With a “classical” survey, only the “stroboscopic” planets are detectable ! Continuous observations • A good phase coverage is determinant to detect the large majority of transits from ground • OGLE: transits discovered • really short periods P ~ 1 day (rare !) • stroboscopic periods • Hot Jupiters: periods around 3 days, depth ~1% Probability of detection of a transit for a survey of 60 days With OGLE For the same telescope with a permanent phase coverage

11. Observing at dome C – Lessons from first two winter campaigns (1) An exceptional coverage … • Confirmation by the first winter campaign of the exceptional phase coverage (cloud coverage, austral auroras) « First Whole atmosphere night seeing measurements at Dome C, Antarctica » Agabi, Aristidi, Azouit, Fossat, Martin, Sadibekova, Vernin, Ziad • Environmental systematic effects considerably reduced: • air mass • timescale of environmental parameters evolution • Expectations for future transits search programs • low scintillation

12. Observing at dome C – Lessons from first two winter campaigns (2) … But a lot of technical difficulties to take into account • Frost – different Behaviour for different telescopes • Differential dilatations inside the telescope • Telescope mounts missfunctionning at really low temperature

13. THE A STEP TEAM

14. A STEP Telescope A STEP Characteristics: Camera use: Defocused PSF PSF sampling: FWHM covering ~4 pixel Time exposure: 10s Readout time: 10s Telescope mount: German Equatorial Astrophysics 1200 With controlled heating Pointing precision tolerated ~.5” Contractor: Optique et Vision ERI CCD DW 436 (Andor) Size 2048 x 2048 Pixel size 13.5 mm 1.74 arcsec on sky

15. A STEP Camera : Andor DW436 • 2048x2048 pixel • Backwards illuminated CCD • Limited intra-pixel fluctuations (Karoff 2001) • Excellent quantum efficiency in red • -USB2 with antarctisable connection

16. A precise photometric telescope at Dome C Telescope tube: INVAR structure With Carbon fiber coverage Thermal enclosure for focal instrumentation 4Mpixel DW436 CCD Wynne Corrector

17. Mode of operation • One field followed continuously (first year) • Flatfields from illuminated white screens • Data storage: ~500 GB /campaign • Data retrieval at the beginning of Antarctic Summer • Redundancy: • Two computers in an “igloo” next to the telescope • Two miror PCs in the Concordia Command Center (fiber link) • Two backup PCs • Semi-automatical: • -Simple control and maintenance every 48 hours

18. Target stellar field for first campaign

19. Data processing Re-use of the major part of BEST (Berlin Exoplanet Search Telescope) data pipeline (Erikson, Rauer)

20. PNP, CSA: 64 k€ (approved) • ANR: 208 k€ (pending) Schedule of A STEP

21. Schedule of A STEP

22. CoRoTlux Stellar field generation with astrophysical noise sources Blends simulation Light curves generation and transit search algorithms coupling

23. Transit Depth Transit Depth • 12 13 14 15 16 17 • Stellar Magnitude Expected results … Using CoRoTlux simulator (end to end stellar field to light curves generator) Guillot, Fressin, Pont, Marmier, … • Considering only planets Giant Planets (Hot Saturn and Jupiter) • Simulation done with CoRoTlux considering 4 stellar fields (1 first year, 3 second year) • Average of 12 Giant Planets for 10 Monte-Carlo draws Exemples of results of two CoRoTlux simulations

24. False Transit Discrimination

25. Many events mimic transits … ! Number of events for 1 CoRoT CCD CoRoTlux (Guillot et al.) Grazing Eclipsing Binaries background eclipsing binaries M Dwarfs target planets background planets Triple Systems target binaries

26. Blends discrimination Within lightcurve: +Secondary transits +Detection level +Exoplanet “diagnostic” or “minimal radius” Tingley & Sackett +Ellipsoidal variability of close binaries (Sirko & Paczynski 2003) + Photocenter of the fluctuation Ground based follow-up: +Radial velocities (provides confirmation by a different method AND planet characterization) – HARPS +Precise photometry with high resolution telescopes and Adaptive optics for critical cases -> 70 to 90 % of transit candidates could be discriminated within lighturves (Estimation from CoRoTlux results – Fressin) ->99+ % false events discrimination goal -> confirmation of most transits with radial velocities … ?

28. Conclusions • A STEP • Is supported by 6 laboratories, French Dome C commission, Exoplanet group, Planetology National Program • Would allow to detect in one season as many transits as all other ground based transit programs in several years. • Will do the photometric test of Dome C for future transit search programs … • CoRoT - Will discover and characterize most of the short period giant planets in its fields, thus largely increase our knowledge of exoplanets - Will provide statistical information on the presence of short periods smaller planets - Could provide the first characterization of super-earth planets Transit research is determinant for exoplanet characterization • Planetary formation and solar system models • A cornerstone for exobiology programs

29. COROTLUX ->Stellar Field generator – Guillot et al (astrophysical noise sources) Point Spread Function and image on CCD – (Fressin, Gay) (instrumental and atmospheric noises – masks/PSF fitting) Light curves generator -> Systematic and environmental effects Search of transits in lightcurves -> Treatment, transit search, discrimination (-> Number of detections) Global ongoing study: Simulation of the optimal transit search program

30. Why searching for transits? Only possible way known to measure an exoplanet radius Combined with radial velocity measurements: • Mass, density, composition Capacity to detect small objets • Jupiter: 1%; Earth: 0.01% Radius measurement (photometry) Mass Measurement (radial velocities) Ground based projects were almost unable to discover objects like Hot Jupiter up today – But there will be great returns as their detection threshold increases